The invention pertains to guideway operated vehicles and, more particularly, to the transfer of electrical signals to a moving vehicle via electromagnetic inductance, without the need for mechanical contact between the vehicle and the guideway. The signal transferred can be used for power, communication or position sensing without deleterious interaction between the various signal.
Transferring electric power to a moving vehicle is an important problem that has been solved in many ways over more than a century of technological development. The most common method is to use sliding contacts, as is done for electric trains, trolley buses and some types of industrial material handling equipment. However, even a vehicle moving on a guideway may move a significant fraction of a meter with respect to the centerline of the guideway, affecting its signal lines or pickup positioning. Typically, a trolley bus uses poles to collect power via sliding contacts, and the contacting system must be mechanically guided separately from the way the vehicle is guided. This method is relatively inexpensive and versatile, but is not suited to very high speeds or to applications where exposed conductors or electrical sparks are not acceptable. An alternate method is to use xe2x80x9cfestoonsxe2x80x9d, i.e., flexible cables. This method works well when the range of motion is limited but is not suitable for vehicles traveling long distances.
Electromagnetic radiation can be used to transfer power long distances at frequencies from microwaves to visible radiation, but this method is not applicable for vehicles that move long distances, often in tunnels or enclosed areas. Other methods have been demonstrated, such as electric arc discharge, but by far the most common alternate method is to use magnetic induction. This is a very old technology, and is the basis of expired patents and also several recent patents including: U.S. Pat. Nos. 4,800,328; 4,836,344; 5,293,308; 5,450,305; 5,467,718; 5,528,113; 5,551,350; 5,619,078; 5,709,291; 5,821,638; 5,839,554; 5,898,579 and 5,939,554.
Communication with a moving vehicle is also an important problem that has been approached in many ways. The most common method is radio communication, such as with cellular telephones or leaky waveguides, but sliding contacts and flexible cables can be used and have many of the same advantages and disadvantages as for transferring power. Inductive transfer of communication signals has been suggested, though bandwidth has proven to be a limitation.
Sensing the position of a moving vehicle is still another very common problem and one that has many solutions, each with major shortcomings. The recent implementation of the Global Position Sensing system has allowed revolutionary changes in this field, but GPS is not a universal panacea. It does not work in tunnels or in the shadow of tall buildings, and its accuracy is limited. The use of differential GPS allows position location to an accuracy of a fraction of a meter, but even this is not adequate for stopping vehicles in stations, for controlling synchronous motors or for common robotic control tasks. Inductive signal transfer has been used successfully and offers many advantages, particularly for vehicles moving on a guideway. However, some inductive transfer technologies require the vehicle to be moving in order to achieve inductive transfer, and this is not acceptable for many applications.
Typically, several of the above tasksxe2x80x94power transfer, communication and position sensingxe2x80x94must be performed for the same vehicle. For example, overhead cranes need power for operating hoists, but they also need to be move along a guideway and be controlled, so that communication must also be implemented. A system such as an Automated People Mover (APM) needs power for propulsion and could benefit from having a communication system for electronic control voice communication. Position sensing is also required for many such applications. To date, the prior art has pieced together disparate systems to accomplish these different tasks, often introducing complicating factors.
In view of the foregoing, it is an object of the invention to provide an improved system and method for powering, locating and/or communicating with a vehicle on a pathway.
It is another object of the invention to provide a simple and effective method and structure to transfer signals of different types with a vehicle on a guideway.
It is another object of the invention to provide a system and method for any of locating and/or communicating with a vehicle with a linear synchronous motor.
One or more of the foregoing desirable objects are achieved in accordance with the present invention by providing an inductive coupling structure for a plurality of signals to effect, in a single system, at least two of the three functions of transferring power, communicating data, and sensing position. In illustrative embodiments, this is done by installing a guideway winding, or set of conductors on a guideway, in such a way that a multiplicity of diverse signals are inductively coupled between the guideway winding and a corresponding vehicle winding, or set of conductors, constituting a transducer assembly that is carried by a vehicle positioned on the guideway.
Aspects of the invention achieve do-coupling between the different signals, allowing such a single-pickup implementation, aplicable to a broad range of guideway-equipment systems. The vehicle may be moving or stationary, and the signals may be coupled in one or both directions. Coupling can be effected without direct electrical contact, through a common region or gap, and the structure provides suitable and precise air gap control for the conductors effecting coupling of each signal. In addition, the windings can be arranged with a topology and/or symmetry to reduce crosstalk or minimize interference between different signals. Aspects of the invention employ patterned conductors on one or more circuit boards to define either or both of the transducer and guideway windings, thus achieving a modular and precise construction.
The coupling conductor or winding for one signal can create a symmetric, periodic or antisymmetric flux pattern that induces at least partially self-canceling and preferably a substantially nulled, signal in the coupling conductor or winding for a different signal. The coupling system arranges sets of inductively coupled conductors with a symmetry that permits two or all three of these signal coupling functions to be done simultaneously with a single transducer structure while avoiding crosstalk or deleterious coupling between the different functions. Preferred implementations utilize conductive patterns on a circuit board, and the board may be shaped to interfit with the mechanical or magnet structure of a linear motor to provide a modular and effective pathway-vehicle system.
Inductive power transfer is preferably carried out at a frequency on the order of ten to fifty kHz at relatively high power levels, typically many watts or even kilowatts or megawatts. The data communication is effected with signal energy of a higher frequency, typically greater than about one MHz, and may involve power levels on the order of a watt, or even less. Inductive position sensing can be done with carrier frequencies that cover the whole range used by both power transfer and communication. The inductive transfer structure of the invention places diverse ones of these signals on a common magnetic structure such that two or more of the signals are effectively multiplexed or simultaneously coupled without mutual interference.
The frequency differences may allow processing techniques such as filtering and demodulation to be of some use in separating different signals, but inductive coupling necessarily creates stray fields, and these present a primary obstacle to inductively coupling plural signals across a localized region, particularly when these include power signals. Aspects of the invention employ symmetry in different forms to achieve cancellations of unwanted signals. The symmetry arrangements may include methods or structures wherein conductors for signals of a first type are arranged and positioned so tho fluxes they generate are oppositely-directed in the vicinity of the coupling conductors for signals of a second type, where tie second coupling conductors are arranged in crosstalk-canceling pairs. Aspects of the invention also contemplate serpentine or zig-zag cult windings that define a periodic pattern of flux regions of alternating polarity, simple loop windings, and multiply-connected or figure-of-eight windings that may be placed in shifted or aligned positions, or otherwise arranged to induce desired signals or null undesired signals. Specific illustrative examples are discussed below.
An aspect of the invention provides for fabricating the inductive coupling systems of the invention using printed circuit technology to define non-interfering winding patterns. This allows precise and relatively complex winding configurations to be made inexpensively on a printed circuit board. Alternate aspects accommodate two or even all three of the desired functions, and may offer improved performance of individual functions beyond the combination of signal coupling. For example, in one important application, position of a vehicle is detected with very high precision, which may be to an accuracy on the order of a micrometer, by manufacturing position coupling conductors on a printed circuit with high precision windings and with registration features that define position with very high accuracy. By sensing the temperature of the circuit board, correction for position errors due to thermal expansion ad contractions of the board may further increase the precision.
In a system combining position sensing with high-speed digital communication, such a printed circuit can be fabricated with additional windings implemented as conductive lead patterns that allow high frequency carriers, modulated by communication signals, to be inductively coupled while nulling interactions with the position sensing conductors.
In another system that transfers power signals at a level of several watts, the power transfer winding can be constructed on a printed circuit board with a conventional etched metallization. For a system of higher power level, i e., carrying a current level greater than the capacity or rating of a conventional printed circuit, a wire winding is bonded to the circuit board substrate, and the board portion provides support and interconnect capability.
The different types of conductor patterns may all be on a common board, or may be on separate boards. Further, the guideway conductor assembly, the vehicle conductor assembly, or both may be entirely or partly implemented as circuit board patterns.
In yet another aspect, the position sensing assembly may be incorporated in and used for control of a linear synchronous motor. A printed circuit may advantageously be formed with cut-outs or slots to adapt the entire printed circuit board to fit in the slots of the iron stator of the linear motor, which thus provides a defined gap and ferromagnetic flux coupling elements for coupling windings on the board to couple position signals.
The foregoing and other aspects of the invention are evident in the drawings and in the text that follows.